Modern threshers, especially large combine-harvesters, have very aggressive threshing equipment, which not only disengage the grains from the stalks but also very heavily comminute the stalks. Thus, a large number of short stalk portions or chaff-like constituents are produced, which heavily load the sieve. This has the disadvantage, that the short stalks can align in the conveying direction and provide no sufficient resistance for the air blower to transport them away.
DE 44 24 383 C2 (=U.S. Pat. No. 5,588,912) describes a cleaning sieve having parallel to the longitudinal axis, channels and air guide channels. The channels and air guide channels alternate. The channels are open on a first side from which they are loaded. An air channel is arranged between the respective two channels, following each other in the transversal direction to the longitudinal axis. The air channel is open to a second side, which faces away from the first side. The channels are delimited by a bottom and laterally following flanks. Openings are provided in the flanks, which are open to the corresponding air guide channel, through which the grains can be transported out.
In this embodiment, each air channel provided between two subsequent channels is connected with two laterally following channels, via openings in the flanks. The cleaning air arriving from the second side is guided through the air guide channels. The cleaning air is also guided through the openings in the flanks to the channels and transports the lighter chaff or stalk constituents out through the channels. Such sieves have a very good cleaning effect. Accordingly, during a normal operation, no blockage is produced at a high output. However, a disadvantage is that the stalk constituents, which are aligned in the longitudinal direction in the channels, can be caught in the openings provided in the lateral flanks. The stalk constituents can penetrate, in an inclined manner, the mating air channel and can settle in the opening of the channels following in the transverse direction. Thus, the air pushes the stalk constituents against the limitations of the openings, so that they cannot be transported out of the channels.